Reactivities of Carbocations and Carbanions

Initiation and propagation rate constants of carbocationic and carbanionic polymerizations can be predicted by the correlation equation log k_{20 °C} = s(N + E), where E characterizes the electrophilicity of carbocations and electron-deficient alkenes, and N characterizes the nucleophilicity of carbanions and electron-rich alkenes. Since the nucleophile-specific slope parameter s is generally close to 1, it can be neglected in a first approximation, and the two-dimensional representation in Figure 3 illustrates the gradual change from carbanionic to carbocationic polymerizations with Hall's “initiation by bond-formation” as the link connecting the two ranges. The value of model studies for understanding ionic polymerizations is illustrated.